Ch.26: Developmental Genetics

Question 1

What are the early developmental stages?

Answer 1

morula- 16-cell stage
blastula- 32-cell stage
gastrula- 64-cell stage

-The uniformity of the dividing cells in a developing animal clearly start to differentiate at the gastrula stage

Question 2

What are morphogens?

Answer 2

molecules that convey positional information and promote developmental change; they can act at the earliest stage of development in the unfertilized oocyte

Question 3

What are homeotic genes?

Answer 3

Genes that specify the final identity of a body region

Question 4

What 2 major axes do most bilateral animals have?

Answer 4

the anteroposterior axis (head-to-tail) and the dorsoventral axis (up-down/front-to-back)

Question 5

What are the 4 definable axes an adult fly emerges from in its pupal case?

Answer 5

-An anteroposterior axis (front-rear or head-tail)
-A dorsoventral axis (up-down)
-A left-right axis
-A proximodistal axis (how the limbs are attached to the body

Question 6

What are the three classes of segmentation genes?

Answer 6

-Gap genes
-Pair-rule genes
-Segment-polarity genes

Question 7

What is the process of segmentation of the organism in early development?

Answer 7

Maternal effect genes g -> gap genes g -> pair-rule genes g -> segment-polarity genes

Question 8

What is a homeotic mutant?

Answer 8

mutant alleles in which
one body part is replaced by another

Question 9

What are polycomb genes?

Answer 9

repress the expression of homeotic genes in regions of the embryo where they should not act

Question 10

What are trithorax genes?

Answer 10

promote the expression of homeotic genes in regions of the embryo where they should act

Question 11

Describe the sexes of nematodes C.elegans

Answer 11

-Male (XO): Produce sperm; An adult male is composed of 1,031 somatic cells

-Hermaphrodites (XX): Produce sperm and eggs; An adult hermaphrodite is composed of 959 somatic cells

Question 12

What are cloned genes used for and from where?

Answer 12

used as probes to identify homologous vertebrate genes from simpler organisms such as Drosophila

Question 13

What are the 2 axes of plants?

Answer 13

-Root-shoot axis: Most plant growth occurs via cell division near the tips of the shoots and the bottom of the roots

-Radial axis: A plant shoot gives off the buds that give rise to branches, leaves and flowers

Question 14

Describe the sex determination in insects

Answer 14

-XX are female, XY and X0 are male
-The X chromosome dictates femaleness and is governed by the Sxl gene
-An insect lacking two X chromosomes is male

Question 15

Describe the sex determination in animals

Answer 15

-XX and X0 are female, XY and XXY are male
-The Y chromosome dictates maleness and is governed by the SRY gene (active)
-An animal with a Y chromosome is male and an animal lacking a Y chromosome is female

Question 16

Describe the sex determination in Drosophilla

Answer 16

the Sxl gene dictates femaleness
and is active in females and inactive in males